Angioplasty procedures have gained wide acceptance in recent years as efficient and effective methods for treating types of vascular disease. In particular, angioplasty is widely used for opening stenoses in the coronary arteries, although it is also used for the treatment of stenoses in other parts of the vascular system.
One form of angioplasty makes use of a dilation catheter which has an inflatable balloon at its distal end. Typically, in coronary procedures, a hollow guide catheter is used in guiding the dilation catheter through the vascular system to a position near the stenosis. Using fluoroscopy, the physician guides the dilation catheter the remaining distance through the vascular system until the balloon is positioned to cross the stenosis. The balloon is then inflated by supplying fluid under pressure through an inflation lumen in the catheter to the balloon. The inflation of the balloon causes a widening of the lumen of the artery to reestablish acceptable blood flow through the artery. In procedures in the peripheral vessels (i.e., vessels other than coronary vessels) the guide catheter may not always be used.
One commonly used type of dilation catheter is referred to as an "over-the-wire" catheter. An over-the-wire catheter is one in which a guidewire lumen is provided in the catheter so that a guidewire can be used to establish the path through the stenoses. The dilation catheter can then be advanced over the guidewire until the balloon on the catheter is positioned within the stenoses. Two commonly used types of over-the-wire catheters are referred to as coaxial catheters and dual or multiple lumen catheters. A coaxial catheter is one in which the guidewire lumen is formed by an inner tube and the inflation lumen is formed between the exterior surface of the inner tube and the inner surface of a coaxially disposed outer tube. A dual or multiple lumen catheter is one in which the guidewire lumen and inflation lumen or lumens are formed of the same material and adjacent to one another in a single tube.
Preferably a dilation catheter will have several performance characteristics. First, there has been a continuing effort to reduce the balloon profile and shaft size of the dilation catheter so that the catheter can reach and can cross a very tight stenosis and also be used in smaller diameter guide catheters. Portions of the dilation catheter must also be sufficiently flexible to pass through tight curvatures especially in the coronary arteries. The ability of the catheter to bend and advance through the vasculature is commonly referred to as the "trackability" of the catheter. A further requirement of a dilation catheter is its "pushability". This involves the transmission of longitudinal forces along the catheter from its proximal end to its distal end so that a physician can push the catheter through the vasculature system and the stenoses. The catheter should be both relatively trackable and pushable. Another requirement of a dilation catheter is a rapid inflation and deflation rate. The inflation lumen of the catheter should be sufficiently sized to allow the balloon to be quickly inflated and deflated. Another requirement is good wire movement. The wire lumen should have a combination of diameter and material which minimizes friction against the guidewire.
It is desirable to design and construct an over-the wire catheter for which each of the above described performance characteristics are defined predominantly by one component. This allows a performance characteristic of the catheter to be altered from one model to another by changing one component without having to change the others. This isolation of one characteristic to one component also allows the size and material of the components to be optimized for the performance characteristic it defines without making compromises for other characteristics effected.
For example, with reference to the dual or multiple lumen catheter, the design choices for the components are limited. Due to the construction of the catheter, the guidewire lumen and the inflation lumen are formed of the same material. This creates a disadvantage in that while a material may be selected to enhance one characteristic of the catheter such as its trackability, another characteristic such as the wire movement provided in the guidewire lumen may be compromised. With reference to the coaxial catheter, the design choices are also limited. The dimension of the inner tube is determined by the size of the guidewire to be used with the catheter. The dimension of the outer tube is dependent upon the dimension of the inner tube. Because of this dependency, as the dimension of the inner tube increases so does the dimension of the outer tube. This relationship between the inner and outer tube influences the design selection and thus the performance characteristics of the catheter. Other factors may also affect the performance characteristics of the above-described catheters.
In addition, the manufacture of these catheters is not very flexible. For example, in a coaxial type catheter, the size of the outer tube must be selected and determined by the size of the inner tube as previously described. Thus, to construct such a catheter for a different size of guidewire both the inner and outer tubes must be changed. With reference to the dual or multiple lumen type catheter, a complete new extrusion must be performed to alter characteristics of the inflation and guidewire lumens.
It is desirable to provide an over-the-wire dilation catheter which overcomes the above-described limitations.